Imagery is everywhere. The eyes are the principal way people gather information about their environment. Audio input is generally the second most common way in which people gather information about their environment. When people can gather information both visually and audibly, each sense reinforces the other. Unfortunately, in many environments rich with visual information, it is difficult to also get audio information because, for instance, if all of the potential audio sources were active in a single environment, there would result an incoherent cacophony. Often these situations arise in public places.